1. Field of the Invention
The present invention relates to the measurement of the heat conductivity of a material and the production of a heat insulating material.
2. Description of the Related Art
Heretofore, heat conductivity has been measured by a plate comparison method specified in JIS A 1412. That is, a test sample and a reference plate are placed one upon the other, a temperature difference is given to them, the difference in surface temperature between them is measured, and the heat conductivity of the test sample is obtained from the ratio and the heat conductivity of the reference plate. In the case of a vacuum insulation material, the heat conductivity of the vacuum insulation material is measured by a so-called reverse vacuum method that it is inspected visually whether the vacuum insulation material swells when the vacuum insulation material is placed in vacuum in a container.
However, the plate comparison method requires a steady state. It takes about 1 hour to reach the steady state, thereby providing an appropriate condition to measure thermal conductivity. Accordingly, it is difficult to measure a large number of products in a short term. With the reverse vacuum method, accurate heat conductivity cannot be measured and when air is contained gradually, it is difficult to judge visually.